(a) Field of the Invention
The present invention relates to a manual valve of a hydraulic pressure control system of an automatic transmission of a vehicle. More particularly, the present invention relates to a manual valve that mechanically controls an exhaust amount based on viscosity and temperature of transmission fluid when the vehicle is shifted from drive to neutral.
(b) Description of the Related Art
In general, automatic transmissions control a plurality of solenoid valves based on speed of the vehicle and throttle valve opening, etc., so as to control a hydraulic pressure. Accordingly, since a shift gear of a target shift range is moved by the hydraulic pressure, shifting occurs automatically.
If a driver moves a lever into a desired shift range, ports of the manual valve of the hydraulic pressure control system are changed such that the hydraulic pressure is supplied from a hydraulic pump to a plurality of operational elements, which are operated by the hydraulic pressure. Such operational elements are selectively operated according to duty cycles of the solenoid valves.
At very low temperatures, since the pressure control valve is controlled by a pressure control solenoid valve so as to control a release pressure, complex control logic is required.
In addition, if the pressure control solenoid valve of the pressure control valve is out of order at very low temperatures, the release pressure may not be controlled. Accordingly, if exhaust time of the transmission fluid is extended, that is, if release of a friction element is insufficient when the vehicle is in neutral, the vehicle may unintentionally move forward.
The above information disclosed in this Background section is only for enhancement of understanding of the background of the invention and therefore it may contain information that does not form the prior art that is already known in this country to a person of ordinary skill in the art.